Golang : How to save log messages to file?

Without log file, system administrators and developers life will be difficult or near impossible to do the work. There is no way to tell where and when a fatal error or crash happened. In this short tutorial, we will learn to save direct any log messages generated by your Golang program into a log file.

The code example below will pipe(direct) any log messages generated by log.Println() functions to the log.txt file.

 package main

 import (
 "log"
 "os"
 )

 func main() {

 // make sure log.txt exists first
 // use touch command to create if log.txt does not exist
 logFile, err := os.OpenFile("log.txt", os.O_WRONLY, 0666)

 if err != nil {
 panic(err)
 }

 defer logFile.Close()

 // direct all log messages to log.txt
 log.SetOutput(logFile)

 log.Println("First log message!")
 }

Hope this short tutorial can be useful to you. Remember to put to archive old log files with timestamp and roll over to new log file to avoid ending up with super big log file.